you didn't mention foe what reason you had undergone TAHBSOO.
The possible causes of vaginal spotting in your case are,
1. If you have undergone hysterectomy
the chances of spreadding of the tissue to vagina is there
2.or it was there previously which was not removed during surgery.
3.If vaginal pack was kept in place for longer time after surgery of forgotten pack can cause but these are extremely rare.
4.Infection may be occurred to the sutures at vault
5.Formation of granulation tissue at the area of suture line.
6.Any fresh infection of external genitalia.
Now you visit your gynecologist get checkup done. By doing speculum examination she can determine the nature of the spots and cause can be make out.